1. Field of the Invention
This invention relates to an electrophotographic image forming apparatus to be suitably utilized as image forming means such as a copying machine, a printer or a facsimile machine and also to an electrophotographic image forming method for using such an apparatus.
2. Related Background Art
Electrophotographic image forming apparatus to be utilized as copying machines and printers comprising a highly durable so-called amorphous silicon photosensitive drum having a photoconductive layer (photosensitive layer) of amorphous silicon (non-single-crystal based on Si atoms, preferably noncrystalline silicon) are popularly known. Particularly, some known electrophotographic image forming apparatus that can print images at a rate of 45 sheets or more per minute comprise an amorphous silicon photosensitive drum and have a configuration as described below.
Such high speed electrophotographic image forming apparatus generally comprise an amorphous silicon photosensitive drum, a primary charger, an image exposure unit, a developing unit, a transfer charger, a separation charger and a cleaning unit. The primary charger electrically uniformly charges the amorphous silicon photosensitive drum. The image exposure unit irradiates the electrically uniformly charged amorphous silicon photosensitive drum with a laser beam in order to draw an electrostatic latent image on the surface thereof. The developing unit develops the electrostatic latent image on the surface of the amorphous silicon photosensitive drum by means of developer. The transfer charger transfers the image developed by means of developer from the amorphous silicon photosensitive drum to a receiving material. The separation charger separates the receiving material from the amorphous silicon photosensitive drum. The cleaning unit removes the developer remaining on the surface of the amorphous silicon photosensitive drum after the transfer and comprises a cleaning blade and a magnetic roller operating as auxiliary cleaning member.
The amorphous silicon photosensitive drum is prepared by forming an about 30 xcexcm thick amorphous silicon photosensitive layer by means of CVD (chemical vapor phase growth) or PVD (physical vapor deposition) on the surface of a base member that is a cylindrical body of aluminum having a mirror-finished surface or a surface provided with a plurality of line grooves having a triangular cross section and arranged around the circumference in parallel with each other. If the surface is provided with a plurality of line grooves having a triangular cross section and arranged around the circumference in parallel with each other, they are arranged at a pitch of about 80 xcexcm and the surface approximately shows a ten-point height of irregularities of Rz=2.4 to 4.0 xcexcm.
However, it is known that, in the case of image forming apparatus comprising an amorphous silicon photosensitive drum of an aluminum base member having a mirror-finished surface, the rotation starting torque of the amorphous silicon photosensitive drum rises in the course of long use so that molten toner can easily adhere to the drum surface or a scraped drum can occur.
On the other hand, in the case of image forming apparatus comprising an amorphous silicon photosensitive drum of an aluminum base member having a surface provided with a plurality of line grooves having a triangular cross section and arranged around the circumference in parallel with each other, the laser beam striking the photosensitive layer can be reflected by the surface of the aluminum base member to give rise to interference fringes, which by turn can produce blurred and/or distorted images.
In view of the above identified circumstances, it is therefore an object of the present invention to provide an electrophotographic image forming apparatus that can form high quality images without the problem of uneven and/or distorted images and that of molten toner adhering to the drum surface and a scraped drum and also an electrophotographic image forming method that can be used with such an electrophotographic image forming apparatus.
It is another object of the present invention to provide an electrophotographic image forming apparatus that can suppress the rotation starting torque of the photosensitive drum and consequently make itself free from the problem of unevenly drawn images, molten toners adhering to the drum surface and a scraped drum after a long use so as to improve the image quality and the durability and also an electrophotographic image forming method that can be used with such an electrophotographic image forming apparatus.
It is a further object of the present invention to provide an electrophotographic image forming apparatus for which a cleaning means including a cleaning blade and a cleaning auxiliary member of a magnet roller for supplying toner to the photosensitive drum is used in order to further improve the durability of the apparatus and also an electrophotographic image forming method that can be used with such an electrophotographic image forming apparatus.
In a first aspect of the invention, the above objects are achieved by providing an electrophotographic image forming apparatus comprising:
a photosensitive drum;
an exposure means for drawing an electrostatic latent image on the surface of the photosensitive drum;
a developing means for developing the electrostatic latent image on the surface of the photosensitive drum by means of developer;
a transfer means for transferring the image developed by means of developer onto a receiving material; and
a cleaning means for removing the developer remaining on the surface of the photosensitive drum after the transfer;
the photosensitive drum being driven to rotate so as to make a cycle of image forming operation proceed;
the photosensitive drum having a photosensitive layer of amorphous silicon with an arithmetical mean deviation of the profile of Ra=0.08 to 0.12 xcexcm.
In a second aspect of the invention, there is provided an electrophotographic image forming apparatus comprising:
a photosensitive drum;
an exposure means for drawing an electrostatic latent image on the surface of the photosensitive drum;
a developing means for developing the electrostatic latent image on the surface of the photosensitive drum by means of developer;
a transfer means for transferring the image developed by means of developer onto a receiving material; and
a cleaning means for removing the developer remaining on the surface of the photosensitive drum after the transfer;
the photosensitive drum being driven to rotate so as to make a cycle of image forming operation proceed;
the photosensitive drum being driven with a rotation starting torque not greater than 0.39 Nxc2x7m.
In a third aspect of the invention, there is provided an electrophotographic image forming method for conducting a cycle of image forming operation by using an electrophotographic image forming apparatus comprising:
a photosensitive drum;
an exposure means for drawing an electrostatic latent image on the surface of the photosensitive drum;
a developing means for developing the electrostatic latent image on the surface of the photosensitive drum by means of developer;
a transfer means for transferring the image developed by means of developer onto a receiving material; and
a cleaning means for removing the developer remaining on the surface of the photosensitive drum after the transfer;
the photosensitive drum being driven to rotate with a rotation starting torque not greater than 0.39 Nxc2x7m so as to make the cycle of image forming operation proceed.